Influenza virus infections have a major impact on human health and the threat of pandemic infections remains imminent. Antibody inducing Influenza A virus (IAV) vaccines are available, however protection is suboptimal and requires annual reformulation of the vaccine. IAV can escape neutralization by preexisting antibodies due to the high rate of mutation in the primary targets of neutralization (hemagglutinin, HA and neuraminidase, NA) and due to its capacity to recombine in non-human hosts. In the absence of neutralizing antibodies, memory CD8 T-cell specific for epitopes located in conserved regions of IAV proteins like the internal components nucleoprotein (NP), polymerase A and matrix protein can confer protection. Recent human challenge studies and longitudinal analyses during the 2009 H1N1 IAV pandemic support the notion that cross-reactive memory CD8 T cells are capable of ameliorating disease when pre-existing antibodies are absent. As most humans carry a small number of these broadly protective memory CD8 T-cells, increasing the number of these cells through boosting is an attractive strategy to bolster their protective capacity. However, memory CD8 T-cells constitute a very heterogeneous population and little is known about how boosting or multiple antigen exposures effects CD8 T-cell mediated protection against IAV, For instance, we have recently reported that the type of booster agent significantly affects the localization and protective capacity of the resulting memory CD8 T-cell population (Sl?tter et al, 2013). Therefore, our long-term goal is to determine optimal memory CD8 T-cell characteristics for protection against IAV and to understand how such memory populations can be generated. In turn, these studies will provide crucial information to optimize broadly protective vaccines for IAV. Specific Aim 1. Determine the molecular mechanisms regulating CXCR3 expression in memory CD8 T cells to enhance airway localization. Specific Aim 2. Determine the impact of repetitive IAV infections on the generation of airway---surveilling, tissue resident and circulatin memory CD8 T cells and their relative contribution in protection from IAV.